Women's professional groups have told the Federal Government its $1.4 billion parental pay scheme is unfair - because it locks out high-income earners who pay the most taxes.

Only women earning less than $150,000 a year can use the taxpayer-funded scheme, which pays new mothers the minimum wage of $606 for 18 weeks.

But a women lawyer's network says the means test discriminates against high-income single mothers and female breadwinners.

And a women miners' group claims the income bar "may deter high-potential women from having children''.

The Women Lawyers' Association of NSW warns the scheme is "open to manipulation''.

"... pregnant women may attempt to manipulate their own income to meet the income test,'' it has told the government's review of paid parental leave.

"While this may seem fanciful, we are aware of one instance where a pregnant lawyer negotiated with her employer to defer the payment of a bonus into the following tax year so that she would fall within the income test.''

PricewaterhouseCoopers director Sue Price, who wrote the lawyers' submission, said any means test should be based on family income rather than the woman's income alone.

"If you're a woman earning $160,000 and you are a sole mother or the main breadwinner you don't get any payment,'' she said.

"The whole idea of a means test on parental leave and childcare is ludicrous when you look at what women's participation in the workforce adds to GDP,'' she said yesterday.

Ms Schwartz said some high-income mothers "work for nothing'' once they have paid taxes and childcare fees.

"A woman on $150,000 is probably paying half of that in tax and half of that again in childcare in order to do her job,'' she said.

"A lot of women are working for nothing.''

Ms Schwartz said childcare costs should be a tax deduction, as a legitimate cost of going to work.

"Isn't childcare the most basic requirement for a working parent to be able to get to work?'' she said.

Women in Mining network chairwoman Kirsty Liddicoat, an engineer who manages a Focus Minerals mine in South Australia, said some highly paid women "might consider not to have children'' unless they could access paid maternity leave.

"I know many families in the mining industry where the female is the high-income earner and the male earns less,'' she said.

"People who earn that much generally pay a lot of tax anyhow.

"Everyone deserves the same treatment and it doesn't matter how much you earn.''

Families Minister Jenny Macklin last week launched a class warfare attack on the Coalition's plan to extend paid parental leave to all mothers.

She said high-income women had fewer babies and were "concentrated in the wealthy suburbs of our major cities''.

Under the Coalition plan, a 1.5 per cent levy on big business would fund maternity leave at full pay for six months, for all working women earning less than $150,000.

Women earning more would have their payments capped at $75,000 over six months.

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